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Create Custom Agent · dotnet | DecimalAI

agent toolingby dotnet

Create Custom Agent

dotnet/create-custom-agent

Source dotnet/skills ↗License MIT

Creates VS Code custom agent files (.agent.md) for specialized AI personas with tools, instructions, and handoffs.

SkillScore91Maintained

Automatic

AI Engineer pack

Last verified 8/9/2026

What it changes

Passed 20 of 22 test cases with the skill, and 11 of 22 without it.

Without skill52%

With skill91%

Checks it passed that the model alone missed

The file uses the .agent.md file extension.
The frontmatter sets user-invokable to false.
The YAML frontmatter configures a handoffs section.

and 12 more in the full report

9 fixed12 passed either way2 still failing0 broke

Pass-rate lift: +39 pp
Tokens: +47%
Agent turns: 0%
Response time: -64%

Model gemini-3.6-flashMeasured 8/9/2026v121 of 23 cases passed with skill · 22 comparable

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/dotnet-create-custom-agent/SKILL.md https://app.decimal.ai/s/dotnet-create-custom-agent/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add dotnet-create-custom-agent, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/dotnet-create-custom-agent/ and pins it in .decimal/skills.lock

decimalai skills add dotnet-create-custom-agent

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/dotnet-create-custom-agent/SKILL.md https://app.decimal.ai/s/dotnet-create-custom-agent/SKILL.md

Raw file: /s/dotnet-create-custom-agent/SKILL.md ↗ · machine-readable summary at /s/dotnet-create-custom-agent.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 8 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 8

Prompt

In the instructions section of a custom agent markdown file, we want to explicitly tell the agent when to invoke the codebase tool. What special chat syntax prefix should be used inside the body text to reference specific tools?

What was checked, without and with the skill
Checked	Without skill	With skill
The instruction text uses the #tool: prefix when referencing tool names.	Missed	Passed

case-15 · gemini-3.6-flash · 8/9/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md272 linessingle file

Create Custom Agent

This skill helps you create VS Code custom agent files that define specialized AI personas for development tasks. Custom agents configure which tools are available, provide specialized instructions, and can chain together via handoffs.

When to Use

Creating a new custom agent from scratch
Scaffolding an .agent.md file with proper frontmatter
Setting up agent-to-agent handoffs for multi-step workflows
Configuring tool restrictions for specialized roles (planner, reviewer, etc.)
Creating workspace-shared or user-profile agents

When Not to Use

Creating instruction files (use .instructions.md instead)
Creating reusable prompts (use .prompt.md instead)
Modifying existing agents (edit the file directly)

Inputs

Input	Required	Description
Agent name	Yes	Descriptive name for the agent (e.g., `planner`, `code-reviewer`)
Description	Yes	Brief description shown as placeholder text in chat
Purpose/Persona	Yes	What role the agent plays and how it should behave
Tools	Recommended	List of tools or tool sets the agent can use
Handoffs	Optional	Next-step agents to transition to after completing work

Workflow

Step 1: Create the agent file

Create a file with .agent.md extension in the agents/ directory:

agents/<agent-name>.agent.md

Step 2: Add YAML frontmatter

Track record

Benchmark

20 / 22

test cases passed, vs 11 / 22 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/3/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

dotnet / skills

.agents/skills/create-custom-agent/SKILL.md

View on GitHub ↗

License MITImported 8/3/2026Version v1

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More skills from the same source and nearby in the registry, with their headline benchmark lift.

Ready to supercharge your AI agents?

See it in action

What's inside

Create Custom Agent

When to Use

When Not to Use

Inputs

Workflow

Step 1: Create the agent file

Step 2: Add YAML frontmatter

Track record

Benchmark

Adoption

SkillSafety

Source

Other skills for the same job

Related skills